Administrator Guide

sFlow
sFlow is a standard-based sampling technology embedded within switches and routers which is used to monitor network traffic.
It is designed to provide traffic monitoring for high-speed networks with many switches and routers.
Topics:
• Overview
• Implementation Information
• Enabling and Disabling sFlow
• Enabling and Disabling sFlow on an Interface
• sFlow Show Commands
• Configuring Specify Collectors
• Changing the Polling Intervals
• Back-Off Mechanism
• sFlow on LAG ports
• Enabling Extended sFlow
Overview
The Dell Networking OS supports sFlow version 5.
sFlow uses two types of sampling:
● Statistical packet-based sampling of switched or routed packet flows.
● Time-based sampling of interface counters.
The sFlow monitoring system consists of an sFlow agent (embedded in the switch/router) and an sFlow collector. The sFlow
agent resides anywhere within the path of the packet and combines the flow samples and interface counters into sFlow
datagrams and forwards them to the sFlow collector at regular intervals. The datagrams consist of information on, but not
limited to, packet header, ingress and egress interfaces, sampling parameters, and interface counters.
Application-specific integrated circuits (ASICs) typically complete packet sampling. sFlow collector analyses the sFlow
datagrams received from different devices and produces a network-wide view of traffic flows.
Implementation Information
Dell Networking sFlow is designed so that the hardware sampling rate is per line card port-pipe and is decided based on all the
ports in that port-pipe.
If you do not enable sFlow on any port specifically, the global sampling rate is downloaded to that port and is to calculate the
port-pipe’s lowest sampling rate. This design supports the possibility that sFlow might be configured on that port in the future.
Back-off is triggered based on the port-pipe’s hardware sampling rate.
For example, if port 1 in the port-pipe has sFlow configured with a 16384 sampling rate while port 2 in the port-pipe has sFlow
configured but no sampling rate set, the system applies a global sampling rate of 512 to port 2. The hardware sampling rate on
the port-pipe is then set at 512 because that is the lowest configured rate on the port-pipe. When a high traffic situation
occurs, a back-off is triggered and the hardware sampling rate is backed-off from 512 to 1024. Note that port 1 maintains its
sampling rate of 16384; port 1 is unaffected because it maintains its configured sampling rate of 16484.
To avoid the back-off, either increase the global sampling rate or configure all the line card ports with the desired sampling rate
even if some ports have no sFlow configured.
Important Points to Remember
● The Dell Networking OS implementation of the sFlow MIB supports sFlow configuration via snmpset.
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